This invention relates to conveyor belts and, more particularly, to link belts constructed of rows of modules pivotally interfitted into an endless link belt and to accessories attached to the belt for conveying product along inclined paths.
Because they are positively driven by sprockets and easy to repair, modular plastic conveyor belts are used widely in place of friction-driven fabric belts. Modular plastic conveyor belts are made up of molded plastic modular links, or belt modules, that can be arranged side by side to form a belt row of selectable width. A series of spaced-apart link ends extending from the leading and trailing ends of the modules includes aligned apertures to accommodate a pivot rod. The link ends along one end of a row of modules are interfitted with the link ends of an adjacent row. A pivot rod extending through in the aligned apertures of the side-by-side and end-to-end connected modules forms a hinge between adjacent rows. Rows of belt modules are connected together by pivot rods into an endless conveyor belt capable of articulating about a drive sprocket.
Many applications require a conveyor belt to transport product along an inclined path. To prevent product from sliding down the conveying surface of a belt as it traverses an incline or decline, belt flights, or cleats, are often used. Generally, the flights in modular plastic conveyor belts are integrally formed with the body of a belt module. U.S. Pat. No. 4,729,469to Lapeyre et al. describes an exemplary righted module molded of plastic material. The flight, in the form of a rectangular plate, extends perpendicularly from the conveying surface of the module. The plane of the flight is normal to the direction of travel of the conveyor belt to support product conveyed along an inclined path.
In belts constructed of integral flighted modules, product conveyed along an inclined path exerts a force against the flight. The force produces oppositely directed forces acting along the hinge axes at each end of the flighted module that tend to tip the module by lifting its uphill end and lowering its downhill end. With the flight tipped back, product can spill. As product spills, the force against the flight and, hence, the degree of tip change, causing jerking motion of the belt. Because the magnitude of the tipping forces at the hinges is proportional to both the force on the flight and the distance of its point of application from the plane of the hinges, the tipping problem is exacerbated with high flights and product having a high center of gravity.
One solution to the tipping problem is to outfit the conveyor with retainer guides having channels that bear against the edges of the belt to prevent modules from tipping. Shortcomings of this solution include the added expense of the retainer guides, the additional drive power required to overcome the friction of the belt edges against the retainer guides, and excessive wear of both the belt edges and the guides.
Another solution to the tipping problem is to tension the belt tightly. Tension along the line of pull of the belt counteracts the tendency of the flighted modules to tip. Consequently, belts in low tension are especially susceptible to module tip. Although flighted modules in a highly tensioned belt are unlikely to tip excessively and spill product, such belts are subject to wear and early failure.